1. Field of the Invention
The present invention relates to measurements of physical characteristics of glass melts in order to predict the quality of the glass produced. In particular, the present invention relates to a set of probes that individually and in combination yield information about the oxygen and alkali activity of the glass melt.
2. Discussion of Background
Probes used for measuring, monitoring, or determining the quality or content of molten mixtures, including glass during production, are well known. Typically, such probes are constructed to generate an electrical signal responsive to the oxygen content of a fluid sample. Stabilized zirconium oxide is often used as a reference electrolyte in such devices.
As is well known, when two gases containing oxygen are located on either side of an electrolyte, a potential difference will be established by the movement of oxygen ions between the gases through the electrolyte. The magnitude of the voltage, E, is given by the Nernst equation: EQU E=(RT/4F) ln (P.sub.1 P.sub.2),
where R is the gas constant; T, the absolute temperature; F, the Faraday constant; P.sub.1, the partial oxygen pressure of the reference gas; and P.sub.2 the partial oxygen pressure of the unknown gas. Thus, the partial pressure of an unknown sample gas present on one side of the electrolyte can be measured if a gas having a known partial pressure is present on the other side of the electrolyte.
Similarly, systems for determining oxygen activity in molten metals, which are based on the same principle, are also known in the art. For instance, Worrell, et al (U.S. Pat. No. 4,428,770) describe a device for determining the sulfur, carbon, and oxygen concentration of molten metal mixtures.
U.S. Pat. Nos. 3,630,874 (Olette, et al.) and 4,007,106 (Hone, et al.) also describe devices for measuring oxygen concentration and activity in molten metal samples by electrochemical means. Olette, et al use a disposable electrochemical cell, which is immersed in the molten sample, to determine the oxygen activity of the sample based on the electric potential across a set of thermocouple terminals.
Perkins, in U.S. Pat. No. 4,313,799, describes a sensor of zirconium oxide for determining oxygen activity in molten glass during the production of textile glass fibers. Also, the exterior portion of the sensor is protected by platinum, thereby extending its life to about one month for noncontinuous use.
Unlike gas probes that are expected to last for long times, probes for molten metals have short term use life expectancies (usually 30 to 60 seconds), as the molten metal environment consumes the probe. Hone et al, in U.S. Pat. No. 4,007,106, details a device used for continuous measurement of oxygen activity and concentration in molten metal samples.
The device in Hone et al provides continuous monitoring without suffering the effects of thermal shock that are usually caused by continuous immersion of a device in molten metal. The device maintains an inert gas atmosphere between the device's reference electrolyte and the molten metal as the device is inserted into the molten metal, thus allowing proper operation without contact between the molten metal and the reference electrolyte.
It is believed that nothing in the foregoing suggests the simultaneous use of more than one probe and measurements taken between the probes to determine molten mixture quality and durability.